+ Reply to Thread
Results 1 to 5 of 5
  1. Aspiring ArchitecT -DeXteR-'s Avatar
    Join Date
    Mar 2011
    Location
    ONLINE
    Posts
    130

    Certifications
    CCNA:R&S
    #1

    Post EIGRP Default Network and Auto Summary relation

    Hi Guys,


    I was practising EIGRP default-network command in my lab today and i'm stuck!


    >After executing the command ip-default network my understanding was the network will be advertised to all eigrp neighbours to use as last gateway of resort.
    >However when i execute the command and check for external network pings it doesn't work unless i use auto-summary command on the router executing the default network command.


    I so doesn't understand this behaviour,shouldn't it be working just after we execute the ip-default network X.x.x.x[ classful] command?


    Please find the logs below :




    Before configuring Auto summary on R1 :






    R1#sh ip route
    Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
    D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
    N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
    E1 - OSPF external type 1, E2 - OSPF external type 2
    i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
    ia - IS-IS inter area, * - candidate default, U - per-user static route
    o - ODR, P - periodic downloaded static route


    Gateway of last resort is not set


    2.0.0.0/32 is subnetted, 1 subnets
    C 2.2.2.2 is directly connected, Loopback2
    * 172.31.0.0/24 is subnetted, 1 subnets
    C 172.31.1.0 is directly connected, Loopback1
    192.168.200.0/27 is subnetted, 1 subnets
    D 192.168.200.0 [90/2297856] via 192.168.100.2, 01:13:40, Serial0/0
    10.0.0.0/29 is subnetted, 1 subnets
    D 10.1.1.0 [90/2681856] via 192.168.100.2, 01:30:35, Serial0/0
    192.168.100.0/29 is subnetted, 1 subnets
    C 192.168.100.0 is directly connected, Serial0/0
    D 192.168.0.0/19 [90/2809856] via 192.168.100.2, 01:15:15, Serial0/0
    R1#sh run
    R1#sh running-config | s eig
    R1#sh running-config | s eig
    router eigrp 1
    network 172.31.0.0
    network 192.168.0.0 0.0.255.255
    no auto-summary
    R1#






    R2#sh ip route
    Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
    D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
    N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
    E1 - OSPF external type 1, E2 - OSPF external type 2
    i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
    ia - IS-IS inter area, * - candidate default, U - per-user static route
    o - ODR, P - periodic downloaded static route


    Gateway of last resort is not set


    172.31.0.0/24 is subnetted, 1 subnets
    D 172.31.1.0 [90/2297856] via 192.168.100.1, 00:00:46, Serial0/0
    192.168.200.0/24 is variably subnetted, 6 subnets, 2 masks
    C 192.168.200.0/30 is directly connected, Loopback1
    D 192.168.200.0/27 is a summary, 01:14:24, Null0
    C 192.168.200.4/30 is directly connected, Loopback2
    C 192.168.200.8/30 is directly connected, Loopback3
    C 192.168.200.12/30 is directly connected, Loopback4
    C 192.168.200.16/30 is directly connected, Loopback5
    10.0.0.0/29 is subnetted, 1 subnets
    C 10.1.1.0 is directly connected, Serial0/1
    192.168.100.0/29 is subnetted, 1 subnets
    C 192.168.100.0 is directly connected, Serial0/0
    D 192.168.0.0/19 [90/2297856] via 10.1.1.3, 01:15:58, Serial0/1
    R2#pi 2.2.2.2


    Type escape sequence to abort.
    Sending 5, 100-byte ICMP Echos to 2.2.2.2, timeout is 2 seconds:
    .....
    Success rate is 0 percent (0/5)
    R2#




    Same goes to R3 as well like R2






    After cofiguring Auto-summary on R1






    R1#sh ip route
    Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
    D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
    N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
    E1 - OSPF external type 1, E2 - OSPF external type 2
    i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
    ia - IS-IS inter area, * - candidate default, U - per-user static route
    o - ODR, P - periodic downloaded static route


    Gateway of last resort is 0.0.0.0 to network 172.31.0.0


    2.0.0.0/32 is subnetted, 1 subnets
    C 2.2.2.2 is directly connected, Loopback2
    * 172.31.0.0/16 is variably subnetted, 2 subnets, 2 masks
    C 172.31.1.0/24 is directly connected, Loopback1
    D* 172.31.0.0/16 is a summary, 00:00:05, Null0
    192.168.200.0/27 is subnetted, 1 subnets
    D 192.168.200.0 [90/2297856] via 192.168.100.2, 01:16:11, Serial0/0
    10.0.0.0/29 is subnetted, 1 subnets
    D 10.1.1.0 [90/2681856] via 192.168.100.2, 01:33:05, Serial0/0
    192.168.100.0/24 is variably subnetted, 2 subnets, 2 masks
    C 192.168.100.0/29 is directly connected, Serial0/0
    D 192.168.100.0/24 is a summary, 00:00:06, Null0
    D 192.168.0.0/19 [90/2809856] via 192.168.100.2, 01:17:46, Serial0/0
    R1#sh run
    R1#sh running-config | s ei
    R1#sh running-config | s ei
    router eigrp 1
    network 172.31.0.0
    network 192.168.0.0 0.0.255.255
    auto-summary
    R1#






    R2#sh ip route
    Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
    D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
    N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
    E1 - OSPF external type 1, E2 - OSPF external type 2
    i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
    ia - IS-IS inter area, * - candidate default, U - per-user static route
    o - ODR, P - periodic downloaded static route


    Gateway of last resort is 192.168.100.1 to network 172.31.0.0


    D* 172.31.0.0/16 [90/2297856] via 192.168.100.1, 00:00:34, Serial0/0
    192.168.200.0/24 is variably subnetted, 6 subnets, 2 masks
    C 192.168.200.0/30 is directly connected, Loopback1
    D 192.168.200.0/27 is a summary, 01:16:40, Null0
    C 192.168.200.4/30 is directly connected, Loopback2
    C 192.168.200.8/30 is directly connected, Loopback3
    C 192.168.200.12/30 is directly connected, Loopback4
    C 192.168.200.16/30 is directly connected, Loopback5
    10.0.0.0/29 is subnetted, 1 subnets
    C 10.1.1.0 is directly connected, Serial0/1
    192.168.100.0/29 is subnetted, 1 subnets
    C 192.168.100.0 is directly connected, Serial0/0
    D 192.168.0.0/19 [90/2297856] via 10.1.1.3, 01:18:15, Serial0/1
    R2#pi 2.2.2.2


    Type escape sequence to abort.
    Sending 5, 100-byte ICMP Echos to 2.2.2.2, timeout is 2 seconds:
    !!!!!
    Success rate is 100 percent (5/5), round-trip min/avg/max = 20/32/44 ms
    R2#

    ThanksDefault-network.jpg
    Reply With Quote Quote  

  2. SS -->
  3. Senior Member
    Join Date
    Sep 2013
    Location
    Sweden
    Posts
    862

    Certifications
    CCNP
    #2
    It's a legacy command that's difficult to work with, but one issue might be that the prefix you are trying to use as the default network isn't in its classful form in the routing table of R1 in the first scenario. So, most likely, it has nothing to do with the auto summary per se, but rather the classful nature of the command. Auto summary simply results in a classful /16 prefix appearing the routing table of R1 in this case. So what will probably work is disabling auto-summary, but making sure that 172.31.0.0/16 is in the routing table by some other means.

    PS.
    I did a test:

    R1 -p2p- R2. 10.0.0.0/24 between the routers. 172.31.0.0/24 as a loopback on R1.

    With auto summary enabled, the routing table of R1 looks like this:

    R1#
    Gateway of last resort is not set

    172.31.0.0/16 is variably subnetted, 2 subnets, 2 masks
    C 172.31.0.0/24 is directly connected, Loopback0
    D 172.31.0.0/16 is a summary, 00:00:06, Null0
    10.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
    C 10.0.0.0/24 is directly connected, Serial0/0
    D 10.0.0.0/8 is a summary, 00:00:06, Null0


    If I issue the default network command on R1 it works:

    R2#show ip route
    Gateway of last resort is 10.0.0.1 to network 172.31.0.0

    D* 172.31.0.0/16 [90/2297856] via 10.0.0.1, 00:00:10, Serial0/0
    10.0.0.0/24 is subnetted, 1 subnets
    C 10.0.0.0 is directly connected, Serial0/0



    However, if I disable auto-summary, it stops working because the /16 classful summary to null0 no longer exists in R1's routing table.

    Now, if I change the subnet mask on the loopback to /16, it should work again.

    R1(config-if)#do show ip route
    C 172.31.0.0/16 is directly connected, Loopback
    10.0.0.0/24 is subnetted, 1 subnets
    C 10.0.0.0 is directly connected, Serial0/0


    And it does:

    R2#show ip route
    Gateway of last resort is 10.0.0.1 to network 172.31.0.0

    D* 172.31.0.0/16 [90/2297856] via 10.0.0.1, 00:00:54, Serial0/0
    10.0.0.0/24 is subnetted, 1 subnets
    C 10.0.0.0 is directly connected, Serial0/0
    Last edited by fredrikjj; 01-09-2014 at 01:24 PM.
    Reply With Quote Quote  

  4. Aspiring ArchitecT -DeXteR-'s Avatar
    Join Date
    Mar 2011
    Location
    ONLINE
    Posts
    130

    Certifications
    CCNA:R&S
    #3
    Yes! I went back to the lab and tried that and it works .


    Thanks!
    Reply With Quote Quote  

  5. Senior Member
    Join Date
    Oct 2007
    Location
    Austin, TX
    Posts
    484

    Certifications
    A+, Network+, MCP, CCNA, CCNA:Voice, CCDA, CCDP, CCNP R/S, JNCIA, JNCIS
    #4
    Would it be fixed by just creating a route 172.16.0.0 /16 to null0 on R1?
    My Cisco Blog Adventure: http://shawnmoorecisco.blogspot.com/

    Don't Forget to Add me on LinkedIn!
    https://www.linkedin.com/in/shawnrmoore
    Reply With Quote Quote  

  6. Aspiring ArchitecT -DeXteR-'s Avatar
    Join Date
    Mar 2011
    Location
    ONLINE
    Posts
    130

    Certifications
    CCNA:R&S
    #5
    Yes that will fix as well
    Reply With Quote Quote  

+ Reply to Thread

Social Networking & Bookmarks